Neuropathic Pain:
Trauma or disease affecting peripheral nerves frequently results in the development of chronic, sometimes intractable, neuropathic pain. Existing treatments for neuropathic pain have limited effectiveness and produce relatively frequent adverse effects. Studies have shown that enhanced pain induced by peripheral nerve injury is associated with increased spontaneous and evoked discharges from injured and/or adjacent nerves. Although this increased afferent discharge is vital in establishing spinal sensitization in the period immediately following nerve injury, the time course of such abnormal afferent activity is inconsistent with the long duration of heightened pain.
Existing treatments for the amelioration of neuropathic pain include both drugs and surgery. Depending upon the specific type of neuropathic pain, drug treatments may range from non-steroidal anti-inflammatory drugs (NSAIDS), to anti-depressants, to agonists and antagonists of neurotransmitters (e.g., glutamate and GABA) to opiate analgesics. These treatments can be effective in some cases (with their efficacy varying from patient to patient) but suffer from side-effects, including toxicity, motor impairment, tolerance, and abuse potential. Moreover, although they can reduce the pain sensations, they seldom result in complete alleviation of the pain. Surgical treatments are typically limited to attempts to relieve pressure on nerve trunks (e.g., in cases of pain from herniated disks or carpel tunnel syndrome) and in these cases they sometimes can be completely effective. However, surgery is much less useful in cases of frank nerve damage, e.g., from accidental or surgical injury to a nerve.